Power supplies are used in a wide variety of applications. A power supply typically receives an input voltage and produces from it an output voltage that is then used to power other electronic components. For example, a power supply may receive an alternating current (AC) input voltage and produce from it a direct current (DC) output voltage that is used to power various integrated circuits and other electronic components. One application in which a power supply is used is electronic metering of electrical energy.
Electronic metering of electrical energy is a maturing technology, and it is desirable to minimize the hardware costs of electronic, electrical energy meters to remain price competitive in the market for such meters. Typically, one of the major cost elements in such a meter is the power supply that develops DC voltage for the various different circuit components within the meter.
The power supply in an electronic, electrical energy meter typically receives the AC line voltage as its input and provides a lower voltage DC output (e.g., 5 or 12 volts DC) that is used to power the internal electronic components of the meter. In higher-end, poly-phase electronic meters, the power supply is typically an off-line switching regulator that can operate over a variety of different AC input voltages. An example of such an off-line switching regulator is described in U.S. Pat. No. 5,457,621. Less complex, single-phase electronic meters typically employ dedicated voltage, linear power supplies.
Today's electronic meters, both poly-phase and single-phase, typically also incorporate wireless communication circuitry. These communication circuits can put a heavy short-term current requirement on the meter power supply during transmit. Many systems are incorporating super-capacitor storage devices to provide the short-term current overloads.
The variable input voltage, off-line switching power supplies employed in higher-end poly-phase electronic meters typically can deliver a high dynamic range of output energy that is sufficient to power wireless communication circuitry. Where short term capacitor storage is needed to assist transmitter current needs, recharge of the capacitors can normally be handled by the off-line supply.
In electronic meters with linear power supplies, the combination of high transmit current requirements for wireless communication and high charge current requirements for storage devices can negatively impact the linear power supply output voltage. With a linear power supply, there typically is not much excess energy available above nominal operating requirements. Wireless communication transmit currents must be delivered by super-capacitor storage devices, but recharge of the super-capacitors is normally restricted to a quasi-trickle charge. The resulting long recharge time can negatively impact the communication performance of the system.
Consequently, there is a need for a power supply design that enables maximum current or voltage draw from a linear power supply to power auxiliary functions, such as wireless communications and/or charging of a super-capacitor, without impacting the ability of the linear power supply to serve its primary power supply functions.